I contacted Microsoft Support about the issue and they sent me an email on how to fix the Timeout Exception.

Symptom:
Users are unable to change the System Status to Complete on the Work Order Schedule, having a System.TimeoutException occurring on a FieldOne Sky plugin when trying to Complete a Work Order Schedule.

Cause:
This issue has been observed when there is a large difference in time between “Travelling” ,“In progress” and “Completed” status for the Work Order Schedules cause the error.

Resolution:
In order to overcome the issue, for the affected Work Orders Schedules, the plan is to remove all the schedule timestamps, while not deleting the initial Schedule timestamp of “Scheduled” solves the issue.

So to solve the problem, you have to go into the Schedule Timestamps and delete all the schedule timestamps while still keeping the original “Scheduled” Timestamp.

Once you have deleted those old Timestamps, you can go ahead and add new timestamps yourself like so:

As you can see the Work Order Schedule has been updated and is now saved and the Work Order has been updated to “Open-Completed”

This is a known bug in FieldOne Sky and it doesn’t look like its getting patched in the near future due to Field Services already being released. So I’m guessing that Field Service doesn’t have this problem. But if you do get a similar issue you can just follow this guide and you will be good to go.

If this solution doesn’t work for you. Then you will have to deactivate the original Work order Schedule and create it again with the same details.